Central Land Council

Rose Report One

Physical Characteristics of Central Australia

This chapter reviews the physical environment of central Australia and highlights the implications of these physical factors on land management practices. Characteristics of the ecology of the study area and the influence of traditional Aboriginal land use practices are presented. This is followed by a discussion of the types of land degradation which occur in relation to physical environmental variables and land management practices.

Climate

An influence of major importance on biological activity throughout the CLC region is rainfall. Central Australia is characterised by low and variable rainfall with the influence of the more northerly summer rainfall belt extending into the region in the north-east. (Appendix 1 contains monthly average rainfall for selected sites in the CLC region.) Most of the study area is arid (receiving <250mm rainfall per year) and semi-arid (between 250 and 500mm per year) however the high variability of rainfall over much of the region must be stressed. Friedel et.al. emphasise that annual average rainfall figures for regions beyond the effect of summer rainfall region can be misleading because they are strongly influenced by a few extremely high rainfalls so that the annual rainfall in an area will be below average for considerably more than 50% of years.

The nature of the rainfall over much of central Australia is such that irregular and often isolated storms contribute substantially to the total rainfall in an area. The flora and fauna which rely on this rainfall must therefore develop strategies which can cope with temporal as well as spatial heterogeneity in the availability of resources. The topography and geology of the landscape further enhance this spatial variability through their influence on the re-distribution of moisture and nutrients following rainfall events.

Any attempts to understand the influence of the climate and landscape on land use practices must take into account the effects of temporal and spatial processes on the distribution of resources. Summer maximum temperatures over the study area frequently exceed 40 degrees Celsius with cool nights especially in the south. During the period of late May to late August frosts can occur in the south but north of 23 degrees of latitude frosts are rare.

Geology and Geomorphology

The physical feature of most influence over land management activities in central Australia is the major relief. Geological features acting in concert with the hydrologic cycle largely determine the occurrence of surface and ground-water which in turn influence patterns of land use and settlement .

The geology of the centre also provides the key to the distribution of mineral resources and at the same time forms many of the features that are the basis of the centre's scenic resource. The Alice Springs area is part of the relatively stable Australian Pre-Cambrian shield with the oldest elements, the "cratonic blocks" exposing granite and metamorphic rocks which form the very basement of the continent. The basement is overlain by the Lower Proterozoic groups which are strongly folded sandstones, greywhackes, and shales with granite intrusions and volcanic rocks. Between the blocks are "intracratonic basins" in which were formed the rocks that now build the major mountain ranges of central Australia.

Sandstones, shales limestones and dolomites were deposited in these basins under the influence of episodes of uplift or downwarping and changes in climatic conditions. During the Upper Paleozoic these sediments were folded in the southern half of the area. A long period of erosion followed before deposition of Mesozoic sediments which underlie an extensive area in the south-east . The processes of erosion and deposition over geological time scales led to the distribution of materials as they are today. Differential erosion of the parent materials left some residual examples of the mantle on divides or where relatively robust cappings were present.

These form plateaus and mesas with relatively steep slopes and surrounding pediments showing weathered zones. The deposition and re-working of the products of this erosion resulted in the development of layered soils over surrounding pediments and valley floors. Over wide areas the mantle was reduced completely to expose the underlying rocks. "The pattern of stripping therefore exposed a range of weathered and unweathered rocks which formed soil parent materials and has thus been a dominant influence over the nature and distribution of soils over much of arid Australia". These geomorphic processes are seen to operate world wide but what is of particular note with reference to the Australian landscape is the length of time that they have been operating.

Soils

"The physical and chemical properties of a soil, and its position in the landscape, influence its inherent productivity, its potential for degradation and the way it should be managed". The soils of the region reflect the long history of the land surfaces on which they occur and from which their parent materials have evolved. The result is that they show a marked degree of weathering and leaching and are generally nutrient poor. (The principal soil types of the study area are presented in Appendix 2).

The region of the Northern Territory which has been covered by land unit and soil type mapping generally excludes most Aboriginal land. For this reason it is difficult to provide information on the relative extent of the soils in the area of interest to this study. The most widespread survey of the soils and land types of the area was carried out by Perry et. al. in 1956−57. The area covered by this survey includes a large portion of the central southern region of the present study area. However, there remains a considerable proportion of the present study area which has not been covered by land system mapping and soil survey work; more specifically most of the Aboriginal land in the area is not mapped, and this is a hindrance to effective decision making about Aboriginal land uses.

The main difference between the soils on Aboriginal land and those on adjacent country such as the pastoral properties is that Aboriginal land is characterised by soils of low fertility, as much of the productive land in the region was taken for European land uses during early settlement. The most extensive soils on Aboriginal land are the red siliceous sands of the Tanami and Simpson desert areas and the red earthy sands on the sand plains. The surface material here is derived principally from sandstone which has been reworked by wind into well sorted fine alluvial sands.

The dune systems present in the deserts are aligned parallel to the predominating winds but are at present largely non- mobile, fixed in place by vegetation. They are considered to have originated during a period of drier climate than at present and as such are considered "fossilised". There are considerable areas of rocky ranges and rugged uplands which are composed mainly of skeletal soils with small inclusions of developed soils. There is generally only light vegetation on these areas with Acacia species and spinifex (Triodia spp.) common. More developed soils occur in isolated areas associated with the rangelands, where water and nutrient materials concentrate.

A feature of the soils which has a strong bearing on their erodibility is their tendency to have low infiltration rates in the dry state. As a consequence heavy rainfall events result in extreme water run-off which flows across the country in broad sheets a few inches deep due to the low relief of many areas. The potential for widespread erosion is therefore quite high in situations where ground cover is disturbed over large areas. In terms of productivity, the alluvial cracking clay flood plains represent the areas of highest possible productivity while retaining a high resilience. This is the result of these areas receiving run-on waters and nutrients, and the fact that the soil is able to regain porosity and therefore water infiltration relatively quickly. Texture contrast soils on the other hand are more liable to scalding and the effects of grazing. These soils tend to occur in close proximity to water courses where the congregation of grazing animals can lead to the breakdown of the light-textured upper soil layer.

Throughout pastoral country many of these soils are in a seriously degraded condition.

Vegetation

Hummock Grasslands

The majority of the vegetation cover is composed of hummock grasslands occurring on the abundant sandplains and dunefields of the Simpson and Tanami deserts, and in many of the arid mountain ranges such as the Petermann Ranges, the MacDonnell Ranges and the James Range. The characteristics common to all hummock grasslands are low nutrient soils and a low water holding capacity. The 'spinifex' grasses of the genera Triodia and Plectrachne are the dominant vegetative components and the growth habit of these species give hummock grasslands their name.

In the north-west the species Plectrachne schinzii (feathertop spinifex) is dominant tending to occur in association with Eucalyptus sp. closer to the subtropical grasslands. Triodia basedowii (soft spinifex) and T. pungens (hard spinifex) occur throughout the region, tending to associate with mulga (Acacia aneura) in the south and east. In general the hummock grasslands are notable for a low number of tree species which tend to occur in association with a high number of shrub species. The most common include species of the genera Acacia, Grevillea, Hakea, and Thryptomene while sub-shrubs are generally soft perennials such as Crotalaria, Dicrastylis, and Solanum species. Grasses are usually annuals or short lived perennials and forbs are generally short lived perennials or ephemerals. The high number of shrub species in the hummock grasslands is indicative of the great diversity of habitats present.

The pattern of succession following disturbance by fire is largely responsible for this diversity. Fires and traditional Aboriginal burning practices over many thousands of years have been an integral part of the formation of the hummock grasslands producing areas with new growth and a flush of ephemeral species adjacent to older unburnt areas with mature spinifex and larger shrubs. This diversity and proximity of habitat types gives hummock grasslands their unique characteristics and an ability to support a great diversity of faunal species.

Woodlands

Woodland communities occur widely throughout the study area associated with regions receiving run-off from ranges and foothills. In the north the increased rainfall provides for the growth of sub-tropical woodlands which are generally Eucalyptus spp. dominated with a dense perennial grass understorey typically of Themeda spp. These native grass pastures are generally of low carrying capacity for cattle. Throughout most of the study area woodland communities dominated by Acacia sp. are common. Mulga (A. aneura) occurs widely with a number of other species such as Ironwood (A. estrophiolata) Bloodwood (Eucalyptus terminalis) and Eremophila species. Gidgee (A. cambagei) occurs in dense stands and tolerates a wide variety of soils. Gidyea (A. georginae) dominated woodlands cover hundreds of square kilometres in the south Barkly area. On alluvial soils a number of species form open woodlands over a variety of grass species. On floodplains characteristic Eucalyptus woodlands composed of River red gum (E. camaldulensis) and Coolibah (E. microtheca) occur. On alluvial plains open woodland is dominated by a variety of species including Whitewood (Atalaya hemiglauca), Supplejack (Ventilago viminalis), and Hakea sp. occur widely.

In both the Barkly and southern Victoria River Downs region Mitchell grasslands (Astrebla spp.) occur on cracking clay soils with generally high fertility. Mitchell grasslands are considered to be the most resilient of Australia's rangeland pastures and as such are an important resource for the pastoral industry. Some small areas of Saltbush (Atriplex sp.) and Bluebush (Maireana sp.) occur in the south of the study area and these are generally not resilient to grazing with the soils tending to be unstable when the vegetation is removed. An important aspect of the vegetation in terms of future management is the use that Aboriginal people make of different species for food and the production of artefacts. In a study of the importance of bush foods for Aboriginal people in the desert homelands Cane and Stanley show that bush foods in the form of seeds, fruits, tubers and bulbs, form a substantial part of people's everyday diet.

Traditionally seeds of Eucalyptus spp. Acacia spp. and several grass species were an important part of the diet. The most important fruit species eaten by Aboriginal people is the bush tomato (Solanum spp.) although wild figs (Ficus platypoda), bush plums (Santalum lanceolatum) and quandong (Santalum acuminatum) are among a number of other species regularly eaten and the tubers of Ipomoea costata, Vigna lanceolata and Cyperus bulbosa are an important component of outstation economies today.

Fauna

The rich and varied habitats of central Australia support a wide variety of mammal and reptile species. Both the introduced and native animals of central Australia provide an important source of food for Aboriginal people, and are also the focus of conservation and research efforts by a variety of organisations.

The hummock grasslands which are a dominant feature of Aboriginal lands are characterised by an extraordinarily rich assemblage of reptile species. At the same time, however, the numbers of bird species in this environment is generally low, as are the numbers of large mammals such as red kangaroos. Throughout southern N.T. there are approximately 61 species of mammals, 144 species of reptiles and 250 species of birds. It is difficult to give precise figures because much of the region has not been surveyed biologically. New species, particularly reptiles, are likely to be discovered in the future; however, it is likely that these figures represent around 98% of extant species. There are also a number of species, particularly mammals, which are known only from previous collections and are now either extinct or restricted to offshore islands which have not been colonised by introduced predators.

Many of the species in the study area occur widely and across different habitats, however, a number are restricted to particular habitats. Many of these species are seen to have declined dramatically to the point of being endangered. The areas that support these species act as "refuges" or "retreat zones" against the changes to the environment caused by the reduction in traditional Aboriginal management practices and the encroachment of introduced land uses such as pastoralism. Morton has examined changes in animal populations since European settlement and factors which are seen to have contributed to these. Since European settlement extinctions in Australian animals have been biased towards mammals. No reptile or bird species are known to have become extinct from the arid zone although the night parrot (Geopsittacus occidentalis) has become extremely rare.

Among the mammals, extinctions have been biased towards those that come from the arid zone. Of the arid zone mammals more medium sized species have become extinct than either large or small species. The factors which have led to these changes are identified as the high spatial variability of production in the arid zone, the introduction of predators, and changes to habitats caused by European herbivores and changes in the fire regime.

Morton suggests that habitat alteration, primarily through the activities of the rabbit (Oryctolagus cuniculus), and to a lesser extent through changes to the fire regime, is the principal cause for these extinctions. A number of introduced animals have become well established in arid central Australia. Pastoralism throughout the region has introduced cattle (Bos taurus and B. indicus) and in some areas there are significant populations of uncontrolled or feral cattle. Feral horse (Equus equus) populations in the Alice Springs region are estimated at approximately 80,000. This figure, however, does not include most of the Aboriginal land in the region which would make the overall figure much higher.

Feral Donkeys (Equus asinus) occur in the Davenport and Murchison Ranges in the north and the Finke and Hugh rivers and eastern MacDonnell Ranges in the south. Camel (Camelus dromedarius) numbers in the Territory as a whole are estimated at around 30,000. The majority of the camel population is located in the desert areas on Aboriginal land. Of the smaller introduced animals the rabbit is the most abundant throughout the south of the study area. Populations are such that harvesting programs have begun at several locations as economic ventures. Rabbit meat is able to find a ready market in local community stores. The impact of high rabbit populations during the early 1900's is seen as a substantial factor leading to the extinction of many arid land mammal species.

The Feral Cat (Felis catus) and Fox (Vulpes vulpes) became widespread in arid inland Australia in the late 1800's to early 1900's. The origin of the cat's introduction to the Australian continent has been a point of some debate, with some authors suggesting that shipwrecks on the western Australian coast may have been responsible. Whatever their origin, cats now extend throughout the arid and semi-arid lands and are extremely successful at surviving in some of the harshest environments in central Australia. Recently the predatory capacity of feral cats has provided a serious cause of concern for scientists attempting to re-introduce populations of the Mala (Lagorchestes hirsutus) into areas of their former habitat in the Tanami desert. Traditional use of animal resources in arid lands by Aboriginal people has been documented in studies from the Great and Little Sandy Deserts, Central Australia, and the western homelands. The animals that form a regular part of the Aboriginal diet include both native and introduced species. Kangaroos, rabbits, cats, euros, bush turkeys, emus, a variety of reptiles and some bird species (eg. budgerigars) are all regular dietary contributions.

A number of species recognised as becoming restricted or recently extinct, such as the Mala, were widely available and used as a food source by Aboriginal people. Today a number of outstations supplement their dietary intake with cattle kept in "killer" herds. Although often available, other large introduced animals such as horses, donkeys and camels are generally not eaten.

Ecology and Influence of Aboriginal Management

A synthesis of the physical and biological characteristics of the study area which constitute its ecology, and therefore the system with which land managers must deal, is provided by Stafford Smith & Morton. The key features identified were the unique climate and landscape of arid Australia and how these act in concert to produce a unique and highly patterned vegetation structure and function.

The spatial heterogeneity which results is a profoundly important factor in determining the patterns of life histories of the animals of the arid lands. The role played by Aboriginal presence in this landscape has begun to be recognised following the realisation of the importance of fire to the maintenance of the arid ecosystem. The implementation of fire management regimes have become the legitimate province of land managers in the arid lands concerned with management for conservation and maintenance of native species.

It is necessary to identify the effects of the Aboriginal fire regime on the pre-Aboriginal biota to understand how important this form of management is to the maintenance of the contemporary environment. Prior to Aboriginal presence in central Australia the fossil record indicates that giant marsupial species known as the megafauna were present here. The cause of their demise is generally regarded as being a combination of climatic change and the effects of Aboriginal fire management practices. Similarly the use of fire by Aboriginal people is implicated in the development of Australia's grasslands although the extent of the role of fire over that of changing climate is still a matter of some debate. In an assessment of the role and use of fire by Aboriginal people, Nicholson identifies several points which should be emphasised.

Fire was a common tool that was used with control and understanding both in domestic life and in the process of obtaining food. The harvesting of food was done in such a way that future food sources were not destroyed. The fire regime evolved from centuries of experience in gaining subsistence directly from the land. Another aspect of the influence of Aboriginal interaction with the flora and fauna of central Australia is the designation of sacred areas within which no hunting or gathering of foods was permitted. These areas have performed an important role by providing refuges for plants and animals during periods of drought. These populations were then able to spread out again to re-populate the country with the return of favourable conditions.

While the influence of Aboriginal practices on the central Australian environment are generally recognised the reasons that particular practices were carried out are not widely appreciated by non-Aboriginal people. The term "land management" is generally used to describe these practices in line with the way non-Aboriginal management of the environment is described. However, it is necessary to realise that Aboriginal practices are not necessarily formulated in the cause (land management practice) and effect (environmental response) model which underlies "land management" practices in the wider society. Land management is generally understood to include the suite of techniques and practices which are applied to land in order to perpetuate particular land uses. For example, pastoral land management requires that a balance is struck between land use and the natural productivity of the land if that land use is to be maintained. The management involved here is to control the access of cattle to the available resources following a cause and effect model. Aboriginal land management includes all of the techniques for living in the arid lands including the use of fire and particular methods of hunting and gathering bush foods. This management is closely integrated with the Aboriginal spiritual view of the world so that the immediate reason given for an activity which we would view as management may be to maintain a tribal law or custom. Aboriginal land management refers to both the management of Aboriginal lands and the management of land by Aboriginal people. Further discussion of these issues and their implications is undertaken in section 4.2.

Land Degradation

Some definitions

The use of the word "land" in this report refers not only to the soil, water and underlying geological structures but includes floral and faunal assemblages and the concepts which may apply to the broader scales of landscape and ecosystem. It is also important to note that for Aboriginal people the concept of "land" also includes other values and notions of responsibility. Land degradation is a term which has a considerable component of value judgment. For example, land may be considered as having little degradation for grazing cattle while that same land may be considered degraded by those who may wish to use it for another purpose such as hunting or gathering bush foods.

The assessment of the condition of a land resource is ultimately a measure of the ability of the land to support an intended land use or the extent to which it exhibits certain values such as biodiversity. Many of the terms used in the discussion of land management issues are substantially influenced by the context in which they are used. Land degradation in the arid lands, and specifically on land used by Aboriginal people, tends to take specific forms because of the land uses that are practised and the particular environmental attributes and values that those uses rely on. This point will be examined further in the following chapters where the impacts of particular land uses are discussed.

It is important to note, however, that defining land degradation on land used for multiple uses is problematic. To date there has been little work done to develop a framework within which competing and overlapping land uses and value systems can be resolved. .

Soil erosion

Because of the physical environment and soils of central Australia, soil erosion tends to take specific forms. (The main forms of erosion and the soil types on which they occur are summarised in Appendix 3). The factor which commonly accelerates all forms of soil erosion is disturbance or removal of the vegetation cover and exposure of the soil surface to the erosive elements of wind and water.

Throughout central Australia pastoralism has been the major disturbance factor leading to degraded vegetation and soil erosion. In 1984 it was estimated that 13% of the land used for pastoralism in central Australia was affected by vegetation degradation and substantial soil erosion in 1975. Another factor leading to vegetation degradation on Aboriginal land is grazing pressure from feral animals. The resultant soil erosion tends to be less widespread than that caused by pastoralism but it often extends into range country and is concentrated around natural waters which are important for Aboriginal people and local wildlife.

Productivity decline

Vegetation degradation is a term which has been used to refer to reductions in plant density, plant vigour, or the proportion of desirable species in a plant community. Vegetation degradation can lead to the sorts of soil erosion discussed above but the impact of vegetation degradation is an issue of special concern on Aboriginal land for other reasons. The condition of the vegetation around outstation communities and on Aboriginal land in general has a direct influence on community health. Loss of vegetation can lead to dust problems and a number of associated health risks. For many communities bush foods are an important component of the diet and provide substantial health and economic benefits to community members. The definition of productivity decline in any particular situation requires that the productivity of an environment is well known before a reduction in that productivity is measurable. The uses of vegetation which are made by Aboriginal people can be interfered with by subtle changes in vegetation composition which can only be seen as productivity decline where their effects on resource availability are known. Before productivity decline can be quantified the full range of uses and therefore products that are available from an environment need to be quantified. For much of Aboriginal land the extent to which bush food and products contribute to the economic and physical well being of Aboriginal people is not well known. Further to this, the changes that have taken place in the environment since European arrival have been so widespread as to make it difficult to find a datum point from which to measure changes in productivity.

Plant and animal species loss

Species loss is and issue of particular concern to conservationists and land managers interested in the long term effects of land management practices. Plant and animal species decline and loss is an indication of significant changes in an ecosystem. Such changes are also of concern to Aboriginal people, particularly where they cause the reduction of loss of species which constitute part of the diet or have special cultural significance. Aboriginal people in central Australia have, over the last century, witnessed the loss of a number of mammal species which had important roles as food sources and as a focus for cultural activity. In many cases these species have now been replaced by the rabbit and other feral animals which are now important parts of the diet.

Implications for land Management

Management practices in the arid lands are constrained by the climatic conditions and landforms of the region. Low rainfall with high variability in the centre has significant influence over more extensive land uses such as pastoralism. Management programs for these areas must have sufficient flexibility to be able to react quickly to changes in climatic conditions. Monitoring of range condition is critical to ensure that vegetation cover does not reach the point where future recovery is jeopardised. The geology and topography of the landscape enhance the spatial variability of resources through their influence on the re-distribution of moisture and nutrients following rainfall events.

The resulting patterned landscape has areas of high resource value and areas where resources are limited or of an ephemeral nature. Land use in these areas is constrained not only by the resources immediately at hand but the relationship of these resources to surrounding areas. For example nutrient rich areas in a landscape of low fertility play an important role for the whole region, as a refuge for plants and animals during dry periods, and as a focal point for cultural activities. Such areas must be managed on their regional significance and context rather than on the resources and productivity afforded by the site in isolation. The geology of the centre also provides the key to the distribution of mineral and scenic resources. It is also the case that geological features often coincide with areas of cultural significance.

This correlation leads to the likelihood that different land uses will compete, and that the management of these areas will become very complex with the interaction of a variety of interests. As we have seen, the most extensive soils on Aboriginal land are those of the sandplains and dune areas. The resources within these areas are limited and land management or development options are also reduced. There are significant areas which remain relatively undisturbed and which provide important habitat for a number of endangered or restricted species. The management of these areas is an issue of priority as a reduction in traditional management practices in these areas has led to significant changes in habitat. A final point of note is that resource uses and management priorities on Aboriginal land are an influence over the sorts of changes in the environment that are considered to be degradation.

Forms of land degradation recognised by non-Aboriginal land managers such as soil erosion, loss of vegetation cover and species of plants and animals occur in varying forms on Aboriginal lands. However, there is a need to examine land degradation issues from an Aboriginal perspective. We do not yet have a clear idea of how land degradation issues are affecting the potential of Aboriginal lands to supply the resources of significance to Aboriginal people.